Load dependent tire inflation and tire deflation is not realized on today's standard long-haul commercial vehicles. The tires are typically inflated to a pressure level recommended for carrying the legally allowed load taking into account the vehicle maximum running speed. However, for a considerable part of the work time vehicles run only with partial loading or completely empty. As a result, the tires are often overinflated for the actual load resulting in excessive wear of tire tread (e.g. on a middle “band” portion of the tread). However, unnecessary wear of the tread can be avoided by controlling the tire pressure based on the actual load, i.e. to deflate the tires to a lower pressure level when the load is low and to inflate the tires when the load is higher. An optimal pressure provides the additional benefit of saving fuel.
Furthermore, as their pressures are checked only occasionally and since leakage reduces the pressure between subsequent checks, the tires tend to be underinflated—at least if the pressure was not checked for some time. However, underinflated tires result in an increased rolling resistance of the tires, which results in more fuel consumption and causes damages of the tire case more often. This is in particular critical, because damages of the tire case can result in an explosion of the tire and thus impairs safety.
Systems for maintaining a tire pressure at a maximum pressure level, independently of the load, are common and are known as automatic tire inflation systems (ATIS).
Moreover, central tire inflation systems (CTIS) are available for off-road and agricultural vehicles to improve off-road or field moving capabilities or to save fuel under off-road conditions. Manual tire pressure selections are likewise known.
For example, US 2007/0068238 A1 discusses a tire inflation system for use with an agricultural implement linked to a work vehicle for movement in a field. The tire inflation system includes a database of soil conditions corresponding to a location, an implement load sensor, a location determiner, a processor and a tire inflation controller so that the processor can determine the proper inflation of the implement tires based on the corresponding factors. US 2012/0221196 A1 discusses another active tire controller device that operates a vehicle either in a city operating condition or in a highway operating condition. Once a highway operating condition is established, an on-board tire pressure controller may be commanded to set a relatively high tire inflation pressure optimizing the tires to minimize rolling resistance and thereby enhancing fuel economy. In a city operating condition, the tire inflation pressure may be returned to normal values optimizing inflation pressure for vehicle dynamic capabilities for manoeuvring, braking or traction.
These systems require a considerable amount of air (e.g. up to 7000 Nltr; normal liter or liter at atmospheric pressure) on a long-haul commercial vehicle combination. However, compressor capacities are limited by confined engine space and costs. As a result, a user has often to wait a long time (e.g. 5 to 30 minutes) before the tire pressure has reached the level needed for the vehicle to safely start its route. Such required time period for inflating the tire(s) is often not acceptable for the user. Furthermore, it is not feasible that a vehicle with low-pressure tire goes into the dock and that a fully laden vehicle with insufficient tire pressure would start the next journey. Tires typically do not tolerate an excessive load when they are on low pressure, nor could the vehicle safely move on. Tire damages would be very likely.
Therefore, there is a demand for an improved way of controlling the pressure of the tire(s) of a vehicle without imposing additional requirements on the air supply system of the vehicle.